The invention relates to a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles.
In heavy commercial vehicles, the parking brake is actuated by what are known as spring force accumulator cylinders (spring-loaded cylinders). Here, the brake actuating force is generated via spring force, with the result that the requirements for a mechanically actuated parking brake are satisfied.
Since the spring force accumulator cylinders are, as a rule, designed to generate very high forces, manual release in the operating case is no longer appropriate. In the case of pneumatically actuated brakes, the parking brake is therefore released by means of compressed air.
In order to make this possible, spring force accumulator cylinders are, as a rule, equipped with a release piston. It is possible by way of this piston, if compressed air is introduced, to compress the spring to such an extent that the brake is released. In order that the parking brake is not engaged while driving, the piston is loaded constantly with compressed air, with the result that the spring cannot be relieved and therefore the parking brake does not start to act.
The most common design is what is known as a combined cylinder. A combined cylinder includes or combines two different brake cylinder types, namely a spring force accumulator cylinder for the parking brake system (PBS) and a compressed air cylinder (usually a diaphragm cylinder) for the service brake system (SBS).
The two cylinders are usually arranged behind one another in an axial direction. The spring force accumulator part, which acts with its piston rod on the piston collar of the diaphragm cylinder and by the latter, in turn, on the brake lever, is arranged behind the diaphragm part of the combined cylinder.
This design requires a relatively large amount of installation space. However, the installation space is being limited increasingly by the introduction of more complex chassis systems, such as independent suspension systems, lightweight axles, etc.
There are therefore efforts to minimize the space requirement for the parking brake cylinder by other designs and methods of operation. To this extent, what is known as a compact combined cylinder affords a more compact design. DE 10 2005 044 708 A1 (corresponding to U.S. Pat. No. 7,523,999 B2) discloses a brake cylinder of this type. In DE '708, the function of the parking brake cylinder is integrated directly into the service brake cylinder. Here, the spring force accumulator spring is no longer actuated via a separate spring force accumulator piston, but rather likewise via the piston of the service brake cylinder. In order to release the parking brake, the SBS piston is loaded for a short time period by way of a special actuation with compressed air.
As described in the preceding text, the parking brake is released as a rule with the aid of compressed air. In addition, however, it also has to be possible to release the parking brake by a manual operation in the case of a pressure loss.
To this end, in the case of conventional combined cylinders, the spring is pulled back with the aid of a threaded spindle (what is known as the “release spindle”). As a result, the function of the service brake cylinder is not imp aired.
Here, the threaded spindle is installed in such a way that, during the manual release of the spring force accumulator brake, the threaded spindle moves out of the cylinder housing as a result of the screwing operation. This results in a clear, visual identifying feature for the manual release state of the spring force accumulator. In the context of safety, it is very important that this state can be detected simply and clearly, since, in this situation, the spring force accumulator is blocked and the parking brake therefore cannot be engaged via the parking brake valve.
In the case of compact brake cylinders, a manually actuable release device is provided to release the spring force accumulator spring manually, which manually actuable release device makes it possible to cancel the spring force accumulator action in the case of a pressure loss, without impairing the SBS function. Furthermore, it is possible to reestablish the PBS action by a manual operation after the release operation.
In the case of the compact combined cylinder, the above-described visual identifying feature cannot therefore be realized according to the manner of the prior art, since the accumulator spring is pulled back with the arresting spindle by a manual intervention. In the normal operating state, the arresting spindle serves to hold the accumulator spring in the “spring force accumulator released” position. Since, however, this spindle is situated completely in the interior of the brake cylinder, its position cannot be used as an identifying feature for the operating state of the spring force accumulator brake.
The object of the invention is to solve this problem.
The invention achieves this object by providing a brake cylinder for pneumatically actuated vehicle brakes, in particular for commercial vehicles, including a spring force accumulator brake section for carrying out parking brake operations by use of a spring force accumulator spring, and a service brake section for carrying out service brake operations which are actuated by compressed air, the spring force accumulator brake section and the service brake section being combined in a housing to form one structural unit. The housing is divided by a piston into two spaces, of which one of the two spaces serves as pressure space for actuating the service brake section. The spring force accumulator spring of the spring force accumulator section being arranged in the further space on the opposite side of the piston. The spring force accumulator spring acts in the space on a further spring force accumulator piston which can be locked with respect to the piston by a pneumatically actuable locking mechanism and can be released from the locking mechanism by release of the latter, and which is connected directly or via further elements to a piston rod for actuating the vehicle brake. After the release of the locking mechanism, the spring force accumulator spring acts between the two pistons and displaces them relative to one another in the case of a parking brake operation. In addition to the pneumatically actuable locking mechanism, the brake cylinder has a manually actuable release device for manually releasing the spring force accumulator brake section and an apparatus which is designed to visually detect the manual release state of the spring force accumulator brake section outside the housing.
Advantageous refinements of the invention are described herein.
The invention provides a mechanism which makes it possible to visually detect the manual release state of the spring force accumulator brake even in compact brake cylinders of the above-described type.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.